In a single stage machine a tire is constructed in a generally continuous process being initially built flat or cylindrical and then shaped to its toroidal shape for final application of the belt and tread assembly either separately constructed or constructed directly on the tire after being shaped. In a first stage machine the tire is constructed in cylindrical or flat band form and then removed to a second stage machine or shaper wherein it is converted to a toroidal shape for final application of components such as the belt and tread assembly.
Whether the machine be single, first or second stage, the beads of the tire must be properly supported and locked for the application or wrapping of the components thereabout. In a single or second stage machine, the bead locks move uniformly toward each other as the tire is expanded and converted from its generally cylindrical to a toroidal or tire shape. Regardless of the type of machine utilized, the beads must be firmly held and precisely positioned both with respect to the axial centerline of the machine as well as the transverse centerline. The beads must be equidistant from the transverse centerline which is through the crown of the tire. In addition, the bead locks in the shaping operation without a shaping sleeve desirably provide an air seal so that air under pressure within the tire will shape it to its desired toroidal shape as the bead locks move toward each other.
Where an elastomeric bead lock is employed, because of the inherent nature of any rubber band, it is difficult properly to seat and control the expansion and contraction of the bead lock to obtain precise centering of the beads both radially and axially. Any rubber band when elongated, narrows in cross section and accordingly the dimensions in the stressed and unstressed conditions are not the same. Moreover, when the bead lock includes an integrally formed shaping bladder, it is difficult to supply such bladder with inflation air pressure without unduly confining it thus precluding it from doing its desired function. The bladder is usually inherently restricted by an inlet or stem offset from the bead lock.
In negative crown tire building, plies of tire material are expanded beneath the bead to reduce the cord count uniformly in the area of the bead to permit the plies to be wrapped more uniformly around the bead without bunching or folding in the bead area. Where the plies include tough reinforcement such as steel or some of the more recent elastomers, considerable force and precision is required properly to seat the plies against the I.D. of the bead and then to wrap and hold the plies uniformly thereabout. This is particularly a problem in large size tires, and even more particularly a problem where complex beads are employed.
To obtain the desired concentricity and axial or lateral stability it has been found that metal contact is preferred. However, to obtain the large expansion force desirable, it has been found that it is preferable to expand the band of the bead lock by direct application of air pressure over a larger area than would be obtainable by utilizing an inflatable tube beneath the expandable bead lock.
The present invention then comprises an improvement over the type of bead lock shown and described in the copending application of George E. Enders, Ser. No. 886,742 filed Mar. 15, 1978 entitled "Tire Building Machine". In such prior application the annular elastomeric band or bead lock is expanded by the closed annular tube positioned radially beneath the bead lock band. While suitable for the construction of certain types of tires, it has been found that the force obrtainable to expand the bead lock is not as great as desirable for the proper construction of other types of tires. Moreover, in the bead lock as shown in the noted prior application, a rubber to metal seat is employed to obtain the desired concentricity and transverse alignment. Again, while suitable for certain types of tires, it has been found that a metal to metal contact is preferable, particularly during shaping wherein substantial axial forces may be exerted on the bead lock. In this manner it is important that the bead lock have axial stability. A prior attempt to provide direct inflation of the bead lock may be seen, for example, in Shichman et al. U.S. Pat. No. 4,081,310.